/*    This file is part of AirSnort.    AirSnort is free software; you can redistribute it and/or modify    it under the terms of the GNU General Public License as published by    the Free Software Foundation; either version 2 of the License, or    (at your option) any later version.    AirSnort is distributed in the hope that it will be useful,    but WITHOUT ANY WARRANTY; without even the implied warranty of    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the    GNU General Public License for more details.    You should have received a copy of the GNU General Public License    along with AirSnort; if not, write to the Free Software    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA*/#include <stdio.h>#include <string.h>#include <stdlib.h>#include "RC4.h" #define NORM(x) ((x) & (N-1))#define SWAP(i,j) do {int t = this->S[i]; this->S[i] = this->S[j]; this->S[j] = t;} while(0)unsigned char Identity[N];void RC4init(RC4 *this) {  memcpy(this->S, Identity, sizeof(unsigned char) * N);  this->i = this->j = 0;}void keyStep(RC4 *this, unsigned char *K,int l) {  this->j += (this->S)[this->i] + K[this->i % l];  SWAP(this->i, this->j);  (this->i)++;}void keyWith(RC4 *this, unsigned char *K, int l) {  int a;  for (a = 0; a < N; a++) keyStep(this, K, l);  this->i = this->j = 0;}int step(RC4 *this) {  (this->i)++;  this->j += this->S[this->i];  SWAP(this->i, this->j);  return (this->S[NORM(this->S[this->i] + this->S[this->j])]);}int SInverse(RC4 *this, int x) {  int a;  for(a = 0; a < N; a++) {    if (this->S[a] == x) return(a);  }  printf("Reality Error #1");  exit(1);}/* Returns the key guess, the assumptions are as follows:   1. The IV is assumed to be IV_SIZE bytes, B is which byte of the key we seek   3. The system is in a 'resolved state' and is at time IV_SIZE+B of keying   4. out is the first output byte of the cypher */int keyGuess(RC4 *this, int B,int out) {   return(NORM(SInverse(this, out) - this->j - this->S[IV_SIZE+B]));}/* Checks if the system is in a state where we can use keyGuess. Assumptions:   1. The IV is IV_SIZE bytes   2. B is byte of the key we seek   3. In key setup as of time IV+B */int isOk(RC4 *this, int B) {  return(this->S[1] < IV_SIZE &&	 NORM(this->S[1] + this->S[this->S[1]]) == IV_SIZE + B);}/* Trys to guess key at location B, Assumptions:   IV_SIZE is the size of the initialization vector.   key is the Initialization Vector+Key   key[x] where x<B+IV_SIZE is known, and in unsigned char *key.   out is the first byte of the cypher output.   This function returns -1 if no guess can be made (often), and even   is made it might be wrong, but the chances of it being right are >= 5%, so   just get a bunch of guesses and look for the answer that shows up the most*/int tryIV(RC4 *this, unsigned char *key, int B, int out) {  int a;  for(a = 0; a < IV_SIZE; a++) {    keyStep(this, key, 16);  }  if (!isOk(this, B)) return(-1);  for(a = IV_SIZE; a < IV_SIZE+B; a++) {    keyStep(this, key, 16);  }  return keyGuess(this, B, out);}void setupIdentity() {  int a;  for(a = 0; a < N; a++) {    Identity[a] = a;  }}